The present invention relates to a single wafer heat treatment apparatus for applying film-forming treatment to the surface of a semiconductor wafer or the like.
Generally, in the process of producing a semiconductor integrated circuit, a desired element is obtained by repeatedly carrying out film-forming and pattern etching or the like to a semiconductor wafer, a glass substrate and the like which are a material to be treated.
For example, the treatment apparatus for applying film-forming to the surface of a wafer includes a batch treatment apparatus capable of applying film-forming treatment to many wafers at once and a single wafer treatment apparatus for carrying out treatment wafer by wafer. Both the apparatuses are properly used depending on the kind of film-forming, the production quantity and the like.
As a single wafer treatment apparatus, there have been known a resistance heating treatment apparatus in which a susceptor for always holding wafers over the whole treatment period of a plurality of wafers, for example, and a lamp treatment apparatus capable of being increased in temperature at high speeds by heat from lamps. The lamp treatment apparatuses so far known are disclosed, for example, in Japanese Patent Laid-Open Publication No. 147428/1984, Japanese Patent Laid-Open Publication No. 343418/1992, Japanese Patent Laid-Open Publication No. 208959/1994, Japanese Patent Laid-Open Publication No. 3229/1991, Japanese Utility Model Laid-Open Publication No. 86935/1986, Japanese Utility Model Laid-Open Publication No. 121732/1992, Japanese Utility Model Laid-Open Publication No. 1996/1997, and Japanese Utility Model Laid-Open Publication No. 63044/1993.
A general lamp treatment apparatus will be described hereinafter by way of example. As shown in FIG. 6, the treatment vessel 2 made of, for example, aluminum is interiorly provided with a heat insulating member 4 in the form of a ring formed of, for example, quartz, and a plate-like place rest (a susceptor) 6 made of, for example, carbon installed on the heat insulating member 4. A semiconductor wafer W is placed on the upper surface of the susceptor 6.
Heating means 12 having a number of heating lamps 10 mounted on a rotary table 8 is arranged under the treatment vessel 2. Radiating energy from the heating lamps 10 are irradiated on the back surface of the susceptor 6 through a transparent window 14 made of quartz at the bottom of the vessel to heat the susceptor 6 so as to indirectly heat the wafer W.
In the outer periphery of the susceptor 6 are provided, for example, a wafer lifter (not shown) which is vertically movable and a plurality of wafer clamps 16. Between the wafer lifter or the wafer clamps 16 is interposed a protective ring 18 made of, for example, aluminum for thermally protecting the lifter and clamps 16.
Further, a shower head portion 20 is installed, at the upper part of the susceptor 6, parallel with and opposed thereto to jet process gas such as silane gas into the treatment vessel 2.
The film-forming process is carried out by supplying the process gas from the head portion 20 to maintain a predetermined process pressure while maintaining the wafer w at a predetermined process temperature. Thereby, a film can be formed on the wafer surface by a predetermined material, for example, such as silicon, silicon oxide film or the like.
Incidentally, it is necessary for obtaining many semiconductor devices having a good electric property to form a film having a good property, and particularly it is necessary to apply a film having an even thickness on the wafer surface.
However, in the above-described conventional treatment apparatus, the wafer w is placed in face contact with the place surface of the susceptor 6, and the wafer W is heated by heat conduction from the susceptor 6. However, since the wafer W is repeatedly subjected to heat treatment many times in the previous process, the back surface of the wafer which appears to be flat is bent and deformed like waving as viewed microscopically. Accordingly, the back surface of the wafer is placed not in face contact with the place surface but in a point contact state. Accordingly, even if the temperature control of the susceptor 6 is carried out with high accuracy, the temperature distribution occurs in the wafer surface resulting therefrom, failing to sufficiently secure the in-plane evenness of a formed film. Particularly, since the deformation mode also differs every wafer, it is the present state that the point contact position also differs every wafer. This results in an unstable element, posing a problem in that the reproducibility of even formed film becomes worsened.
Further, the susceptor 6 shown in FIG. 6 need be placed without being secured to the heat insulating member 4 to allow a thermal expansion. Therefore, a partial clearance is created between the lower surface of the susceptor 6 and the heat insulating member 4 so that the process gas flows into the back surface of the susceptor 6 through the clearance as shown in FIG. 6, and the formed film 22 is adhered to the back surface of the susceptor 6 and the inner surface of the transparent window 14 which are in a high temperature state. Since the formed film 22 changes the permeability and the emissivity from the heating lamps 10, the heat efficiency lowers, the temperature distribution of the wafer occurs, the film thickness increases as the number of wafers to be treated increases, and the reproducibility of heat treatment lowers.
In this case, a thermocouple (not shown) is embedded every zone into the susceptor 6 for the temperature control. It is the present state that the position of the thermo-couple is locked while the adhesion of the formed film has a two dimensional extension, and only the thermo-couple is not enough to cope with the temperature control thereof.
In the apparatus shown in FIG. 6, the spacing L1 between the protective ring 18 at thermally the same level as the treatment vessel 2 and the circumferential portion of the susceptor 6 is necessary, but for the purpose of miniaturizing the apparatus, the spacing L1 is very narrow, for example, about a few mm. Therefore, even if the mounting position of the susceptor 6 is deviated by only about 0.5 mm, it receives an uneven thermal influence from the protective ring 18 externally thereof.
As a result, the heat resistance between the peripheral edge portion of the susceptor 6 and the protective ring 18 is not even but uneven in the circumferential direction, and the temperature distribution is deviated as shown in FIG. 6, resulting in the occurrence of uneven temperature distribution. Area 23 surrounded by the chain line in FIG. 7 indicates an area whose temperature is lower than other portions. Such an uneven temperature distribution causes the in-plane evenness of the film formed on the wafer to lower.
The unevenness of the film thickness as described above poses a significant problem as the size of the wafer increases from 6 inches to 8 inches, and with the trend of higher density and higher fineness of IC, and thinner film.